Mirena side effects

Elvia
I got my Mirena IUD in December . It's been a month and no period yet. I did experience headaches the first weeks, and spotting but that's about it. Recently I've been feeling nauseous and I'm scared that I might be pregnant . I also couldn't feel the strings yesterday when I checked and now I'm freaking out more! I have an appointment to make sure it's in place this weekend .